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Phico 52 volume control problem - Printable Version

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Phico 52 volume control problem - jerryhawthorne - 09-09-2013

Working on this radio for a friend. The problem is the volume control comes on loud and smooth from the last quarter of rotation.
Please look at the attached link and the 52 schematic, the one with the center tap at ground.
Now, I have removed the pot and everything test out well, proper resistance from end to end and nice resistance change from both ends to ground.
Looks like the coil on one side is good and the other to the 200 ohm is good. Any ideas? I'm stumped as often I am.Icon_crazy
Thanks, Jerry

http://www.nostalgiaair.org/PagesByModel/638/M0029638.pdf

RE: Phico 52 volume control problem - Radioroslyn - 09-09-2013

What you got is a volume control that does two things. The top half controls the level of RF that go to the input to the mixer. The bottom controls the cathode bias on the IF amp. So I would check #34 and the 35 tube. When you look at the schematic it does look confusing with the B+ going to ground thru the volume control.
GL
Terry

RE: Phico 52 volume control problem - jerryhawthorne - 09-09-2013

Thanks Terry. I did pull the 35 tube earlier and it tested real wimpy. Just surprised and checked it due to the set falling dead above about 1200KC. Waiting for a new one. I will check #34 what ever that is after I check the schematic.
Thanks and still like your Falcon.
Jerry

RE: Phico 52 volume control problem - Arran - 09-09-2013

It looks like the model 52 just uses a simple shunt volume control in the antenna circuit, basically it controls gain by the wiper moving closer or further away from ground potential. It's the one in the model 50 that also controls cathode bias on one of the #24 tubes, the model 50 is a cheap TRF set, the model 52 is a superhet.
Regards
Arran

RE: Phico 52 volume control problem - jerryhawthorne - 09-09-2013

Aaron, thanks for your response but I think you were looking at the schematic for the 51. The 52 (on the same link) is not a simple shunt on the RF (antenna) but as indicated by Terry, actually controls not only the RF but also something in the IF section. The center tap of the volume control is at ground.

Jerry

RE: Phico 52 volume control problem - Radioroslyn - 09-09-2013

Yes I understand that I'm looking at the bottom schematic which is the one for the model 51 and 52.
It does control the IF gain thru the volume control.
Terry

RE: Phico 52 volume control problem - jerryhawthorne - 09-09-2013

Terry, I did study the schematic a little more and #34 is a bakelite with a 200 ohm and a cap, also labeled as #34. The radio did the same thing prior to restuff so I think I need to look a little longer along that line towards the IF. You have given me some ideas and thanks. I understand you are looking at the right schematic.
Jerry

PS Aaron sorry when I indicated you were looking at the 51, I should have said the 50. The 51 and 52 seem to be the same and both have a center tap at ground.

RE: Phico 52 volume control problem - Radioroslyn - 09-09-2013

One other thing to check make sure the volume control is the proper value. Someone may have replaced it with one out a more modern set which would be a much high value. That would cause your problem.
Terry

RE: Phico 52 volume control problem - jerryhawthorne - 09-09-2013

Thanks Terry, it is dead on for total resistance but upon opening it it appears to have two different types of windings from one end to the middle. Strange looking. One end clearly wire, the other black looking stuff that looks like might a winding underneath.
Jerry

RE: Phico 52 volume control problem - Radioroslyn - 09-10-2013

Ok If you hook an analog ohm meter to it what does the taper look like? Is even?? If not we are back to the tube or a bias problem
Terry